I would quite like to see the modularisation and standardisation of sofas to facilitate the market in fitted covers. Beds, duvets and pillows have standard sizes.
In the shortterm, I would like a sofa that uses fitted bed sheets and pillow cases. The sofa uses a single mattress for the bit you sit on, and has back cushions the size that will fit pillow cases. As there are already so many colours and patterns of sheets and pillow cases out there, this would allow significant customisation of the sofa. (and ease of washing)
I'm sure there is a business opportunity for a company to make sofa frames and cushions that fit standard size fitted sheets and pillow cases. The sofa arms are the most difficult, possibly a cushion that sits vertically in a slot between the mattress and a wooden wall, or one that forms an 'n' shape over a wooden arm.